^ my bad so if your flight to singapore is at 545pm then leave around 2pm. better early than late sa airport.
yes, Bandung weather is quite like Tagaytay and I do suggest that you visit Bandung than Jakarta dahil puro malls lang nga sa Jakarta
re: volcano crater, are you referring to Tangkupan Perahu? then its about 1 1/2 - 2 hours from Bandung.
i haven't been there myself so i can't give you pointers. some reviews are posted in TripAdvisor so take heed na lang on the comments.